Why would the support tower break if the motor locked up, especially going towards the wind? There are inoperative windmills in Rio all the time on windy days -- they don't all explode if the blades stop spinning on a windy day. It seems more likely that there was a fatal flaw in the tower, and once it started to bend, the blades hit it and the whole thing exploded.

They are actually designed to spin slow. They have brakes on them so they don't spin out of control. This one lost it's brakes and that's why they call it a run away. They also will shut em down in high wind. I've seen one break in person but I've never seen one explode like that

I think its a lockup because if you take something with that much rotational mass and momentum and suddenly stop it, that energy has to go somewhere. It looked to me like one of the blades started to break off causing the whole thing to distort from unequal load. With a 200' blade weighing many tons, it wouldn't be inconceivable to have it tear the tower to pieces. Perhaps one of the blades hit the tower as well, after all, the tower is downwind of the blades.

I watched it again and the only thing that would make sense is that the wind load pushed the blade into the tower. You can see the crease in the pole where the blade hit.